DeForest Columbian 7D634 hum

[Robert]

Hi everyone,

Just found this amazing resource!

As the title says, this baby is humming.

I picked it up about 30-odd years ago at a flea market in Montreal for 50 bucks. I replaced a few of the tubes (Radio Hovsep in Montreal still had tons), and it worked fairly well. Ever since shortwave started taking a nosedive, I stopped using it, and it was just a lovely piece of furniture.

I’m now in Victoria (where electronic parts are impossible to find locally), and I’ve decided to resurrect it.

There was some serious 60Hz hum when I fired it up, so I yanked out the electrolytic cans and replaced them with modern caps. 60Hz hum gone, mostly.

Now there’s a (probably) 120Hz hum that sits at noise level, then ramps up when a station is pulled in on AM (there’s only 1 in Victoria)

I’m not sure where to go from here. I’ve also swapped out the 3 high voltage .1uf caps, but it didn’t do anything.

Any and all suggestions would be appreciated.

For context, I’m a 68 year old retired microwave radio hardware designer (2-18 GHz LNAs, mixers, PAs, filters, etc), but know virtually nothing about vacuum tubes.

Thanks

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